The natural history and tailored treatment of ACL injury

The fate of the injured anterior cruciate ligament (ACL) is variable. The spectrum of injury ranges from partial sprain (grade 1 or 2) to a complete disruption (grade 3), which may occur in isolation or in combination with injury to other structures in the knee. Postinjury symptoms of knee instability usually depend on the degree of joint laxity and the athletic demands of the individual. If an ACL injury is left untreated, repeated episodes of subluxation can inflict further intra-articular damage, with an increased risk of developing osteoarthritis. Predicting the outcome after ACL injury is difficult, and treatment should be individualized.